Abstract:

A photovoltaic electrochromic device includes a semi-transparent thin-film
solar cell substrate, an electrochromic solution, and a transparent
non-conductive substrate, wherein the electrochromic solution is located
between the transparent non-conductive substrate and the semi-transparent
thin-film solar cell substrate. The semi-transparent thin-film solar cell
substrate includes a transparent substrate and a plurality of thin-film
solar cells, wherein the anodes and the cathodes of the thin-film solar
cells are also used as the anodes and the cathodes of the photovoltaic
electrochromic device. Because a driving voltage of the electrochromic
solution is low, the thickness of an intrinsic layer in each of the
thin-film solar cells can be thinned, which increases the transmittance
of the photovoltaic electrochromic device. Besides, the current output of
the photovoltaic electrochromic device can be controlled by an additional
output switch layout coupled with the thin-film solar cells.

Claims:

1. A photovoltaic electrochromic device, comprising:a transparent
non-conductive substrate;a semi-transparent thin-film solar cell
substrate, comprising a transparent substrate and a plurality of
thin-film solar cells, wherein an anode and a cathode of each of the
thin-film solar cells also serve as an anode and a cathode of the
photovoltaic electrochromic device; andan electrochromic solution
disposed between the transparent non-conductive substrate and the
semi-transparent thin-film solar cell substrate.

2. The photovoltaic electrochromic device as claimed in claim 1, wherein
the thin-film solar cells are arranged in array or in stripe, or a
combination thereof.

3. The photovoltaic electrochromic device as claimed in claim 1, wherein
the electrochromic solution comprises at least one redox-type organic
molecule electrochromic material and at least one solvent.

4. The photovoltaic electrochromic device as claimed in claim 3, wherein
the redox-type organic molecule electrochromic material is a material
selected from a material group comprising a cathodic electrochromic
material and an anodic electrochromic material, or a combination thereof.

5. The photovoltaic electrochromic device as claimed in claim 4, wherein
the cathodic electrochromic material is one selected from the group
consisting of methyl viologen, ethyl viologen, benzyl viologen, heptyl
viologen, propyl viologen, derivatives thereof and a mixture thereof.

6. The photovoltaic electrochromic device as claimed in claim 4, wherein
the anodic electrochromic material is one selected from the group
consisting of dimethylphenazine,
N,N',N,N'-tetramethyl-p-phenylenediamine, phenylene diamine, derivatives
thereof and a mixture thereof.

10. The photovoltaic electrochromic device as claimed in claim 3, wherein
the electrochromic solution further comprises a polymer.

11. The photovoltaic electrochromic device as claimed in claim 10, wherein
the polymer is one selected from the group consisting of polyethylene
oxide, polypropylene oxide, polymethylmethacrylate and a mixture thereof.

12. The photovoltaic electrochromic device as claimed in claim 1, wherein
a redox voltage of the electrochromic solution is smaller than 3V.

17. The photovoltaic electrochromic device as claimed in claim 1, wherein
each of the thin-film solar cells comprises a semiconductor stacked layer
between the anode and cathode and further comprises a plurality of
passivation layers formed on a plurality of sidewalls of the
semiconductor stacked layer.

18. The photovoltaic electrochromic device as claimed in claim 1, further
comprising a reflective layer deposited on the transparent non-conductive
substrate to form a mirror surface.

19. The photovoltaic electrochromic device as claimed in claim 18, wherein
a material of the reflective layer comprises one of silver and aluminum
thin film coatings.

20. The photovoltaic electrochromic device as claimed in claim 1, further
comprising a plurality of thin-film transistors for actively controlling
the thin-film solar cells.

21. A photovoltaic electrochromic device, comprising:a transparent
non-conductive substrate;a semi-transparent thin-film solar cell
substrate, comprising a transparent substrate and a plurality of
thin-film solar cells, wherein the anodes and cathodes of the thin-film
solar cells also serve as an anode and a cathode of the photovoltaic
electrochromic device;an output switch layout coupled to the thin-film
solar cells for controlling a current output from the thin-film solar
cells; andan electrochromic solution disposed between the transparent
non-conductive substrate and the semi-transparent thin-film solar cell
substrate.

22. The photovoltaic electrochromic device as claimed in claim 21, wherein
the thin-film solar cells are connected in parallel with the output
switch layout.

23. The photovoltaic electrochromic device as claimed in claim 21, wherein
the thin-film solar cells are connected in series with the output switch
layout.

24. The photovoltaic electrochromic device as claimed in claim 21, wherein
the output switch layout is further connected with a DC/AC inverter for
converting a current provided by the thin-film solar cells into general
electricity.

25. The photovoltaic electrochromic device as claimed in claim 21, wherein
the output switch layout is further connected with a DC charge storage
device for storing a direct current provided by the thin-film solar
cells.

26. The photovoltaic electrochromic device as claimed in claim 21, wherein
the electrochromic solution further comprises at least one redox-type
organic molecule electrochromic material and at least one solvent.

27. The photovoltaic electrochromic device as claimed in claim 26, wherein
the redox-type organic molecule electrochromic material is a material
selected from a material group comprising a cathodic electrochromic
material and an anodic electrochromic material, or a combination thereof.

28. The photovoltaic electrochromic device as claimed in claim 27, wherein
the cathodic electrochromic material is one selected from the group
consisting of methyl viologen, ethyl viologen, benzyl viologen, heptyl
viologen, propyl viologen, derivatives thereof and a mixture thereof.

29. The photovoltaic electrochromic device as claimed in claim 27, wherein
the anodic electrochromic material is one selected from the group
consisting of dimethylphenazine,
N,N',N,N'-tetramethyl-p-phenylenediamine, phenylene diamine, derivatives
thereof and a mixture thereof.

33. The photovoltaic electrochromic device as claimed in claim 26, wherein
the electrochromic solution further comprises a polymer.

34. The photovoltaic electrochromic device as claimed in claim 33, wherein
the polymer is one selected from the group consisting of polyethylene
oxide, polypropylene oxide, polymethylmethacrylate and a mixture thereof.

35. The photovoltaic electrochromic device as claimed in claim 21, wherein
a redox voltage of the electrochromic solution is smaller than 3V.

40. The photovoltaic electrochromic device as claimed in claim 21, wherein
each of the thin-film solar cells comprises a semiconductor stacked layer
between the anode and cathode and further comprises a plurality of
passivation layers formed on a plurality of sidewalls of the
semiconductor stacked layer.

41. The photovoltaic electrochromic device as claimed in claim 21, further
comprising a reflective layer deposited on the transparent non-conductive
substrate to form a mirror surface.

42. The photovoltaic electrochromic device as claimed in claim 41, wherein
a material of the reflective layer comprises one of silver and aluminum
thin film coatings.

43. The photovoltaic electrochromic device as claimed in claim 21, further
comprising a plurality of thin-film transistors for actively controlling
the thin-film solar cells.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims the priority benefit of Taiwan application
serial no. 97125127, filed on Jul. 3, 2008. The entirety of the
above-mentioned patent application is hereby incorporated by reference
herein and made a part of specification.

[0005]What we call an electrochromic device is a device constituted of
conductive materials for performing color changing when an electric field
or current is applied to cause a reversible redox reaction. The
fabrication of an electrochromic device should satisfy the following
requirements: under different voltages, colors of the electrochromic
device should be easily recognizable; the change of colors should be
rapid and uniform; the reversibility of the color changing of the device
should be repeatable for at least ten thousand times; and the device
should have high stability. Commonly-used electrochromic devices are
surface confined thin-film electrochromic devices and solution-type
electrochromic devices.

[0006]A surface confined thin-film electrochromic device is formed by a
top transparent substrate, a bottom transparent substrate, and an
electrochromic multi-layer disposed therebetween. Specifically, the
electrochromic multi-layer has a structure similar to a battery, which at
least has five coated/deposited layers of different functions. The
aforesaid five coated/deposited layers are a transparent conductive
layer, an electrochromic layer, an electrolytic layer, an ion storage
layer, and another transparent conductive layer. The solution-type
electrochromic device has a simpler structure and is formed by a top
transparent conductive layer and a bottom transparent conductive layer,
which are bonded by an epoxy resin adhesive in a direction facing an
electrode layer, and an electrochromic organic solution is disposed
between the top and the bottom transparent conductive layers. The
solution includes oxidation-type or reduction-type electrochromic organic
molecules, a polymer electrolyte, and a solvent.

[0007]After years of research, only electrochromic rear-view mirrors have
been commercialized. Other large-sized electrochromic devices 100 still
face the problem of non-uniform color changing, which is also called an
iris effect, as shown in FIG. 1. The explanation of the iris effect is
based on FIG. 2. FIG. 2 illustrates a general electrochromic device 200,
which is constituted of two transparent conductive substrates 210 and an
electrochromic solution 220 disposed therebetween. When the electricity
is provided from an electrode 230 disposed on the periphery of the two
transparent conductive substrates 210, the difference in the path length
of the electric fields in the center and the periphery of the plane
electrochromic device 200, causes variation in the impedance; the
difference in impedance is illustrated in FIG. 1. The gradual homocentric
change of color concentration is displayed from the periphery to the
center of the electrochromic device 200, which affects the uniformity of
color changing.

[0008]To extend the application of electrochromic technology, researches
that integrate photovoltaic technology have provided diverse directions
for development. For instance, building integrated photovoltaic (BIPV)
solar cells may be cooperated with the electrochromic technology to
automatically adjust the colors of electrochromic windows to reduce
indoor heat, based on indoor and outdoor illumination differences, which
does not require any additional power supply. As power saving becomes
more and more important, such an application has become a new trend.

[0009]For example, U.S. Pat. No. 5,377,037 has disclosed an electrochromic
device which integrates silicon thin-film solar cells with electrochromic
materials. In view of the structure thereof, silicon thin-film solar
cells of a tandem structure, an electrochromic device, and an
electrolytic layer are sequentially disposed between two transparent
conductive glass substrates. Finally, bleed resistor are connected in
series outside the two transparent conductive glass substrates of the
tandem structure, so as to activate or deactivate the voltage which
drives the electrochromic device when the silicon thin-film solar cells
generate power. Although the double-side electrode structure can
integrate the electrochromic device with solar cells, inorganic materials
require greater charge density and larger voltage for performing color
changing. Inevitably, the intrinsic layer needs to be thicker, so as to
enhance the efficiency of photovoltaic conversion. Multi-junction stacked
tandem cells may even be applied to increase the open circuit voltage
(Voc) of the silicon thin-film solar cells. Consequently, the
transmittance of the silicon thin-film solar cells is reduced.

[0011]The present invention provides a photovoltaic electrochromic device
which includes a semi-transparent thin-film solar cell substrate, an
electrochromic solution, and a transparent non-conductive substrate,
wherein the electrochromic solution is disposed between the transparent
non-conductive substrate and the semi-transparent thin-film solar cell
substrate. The semi-transparent thin-film solar cell substrate includes a
transparent substrate and a plurality of thin-film solar cells, wherein
the anodes and cathodes of the thin-film solar cells also serve as an
anode and a cathode of the photovoltaic electrochromic device.

[0012]The present invention further provides a photovoltaic electrochromic
device which includes a semi-transparent thin-film solar cell substrate,
an electrochromic solution, a transparent non-conductive substrate, and
an output switch layout, wherein the electrochromic solution is disposed
between the transparent non-conductive substrate and the semi-transparent
thin-film solar cell substrate. The semi-transparent thin-film solar cell
substrate includes a transparent substrate and a plurality of thin-film
solar cells, wherein the anodes and cathodes of the thin-film solar cells
also serve as an anode and a cathode of the photovoltaic electrochromic
device. The output switch layout is coupled to the thin-film solar cells,
so as to control a current output from the thin-film solar cells.

[0013]According to the present invention, the thin-film solar cells are,
for example, distributed in array or in stripe on one substrate, so as to
achieve uniform color changing. Moreover, in the present invention, the
electrochromic solution requires lower redox voltage, and thus the demand
for power generated by the thin-film solar cells is lowered. As a
consequence, the thickness of the material of the solar cell thereof is
reduced to increase the transmittance of the whole device.

[0014]To make the above features and advantages of the present invention
more comprehensible, several embodiments accompanied with drawings are
described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and constitute a
part of this specification. The drawings illustrate embodiments of the
invention and, together with the description, serve to explain the
principles of the invention.

[0018]FIG. 3A is a schematic top view of a photovoltaic electrochromic
device according to one embodiment of the present invention.

[0019]FIG. 3B is a schematic cross-sectional view along Line B-B in FIG.
3A.

[0020]FIG. 3c is a schematic cross-sectional view of another variation of
the photovoltaic electrochromic device in FIG. 3B.

[0021]FIG. 4 is a schematic perspective view of the photovoltaic
electrochromic device in FIG. 3B.

[0022]FIG. 5 is a curve diagram showing an electrochromic cyclic
voltammogram of an electrochromic solution.

[0023]FIG. 6 is a schematic cross-sectional view of a semi-transparent
thin-film solar cell substrate used in one of the embodiments.

[0024]FIG. 7A is a schematic cross-sectional view of a photovoltaic
electrochromic device according to the second embodiment of the present
invention.

[0025]FIG. 7B is a schematic cross-sectional view of another variation of
the photovoltaic electrochromic device in FIG. 7A.

[0026]FIG. 8A is a schematic cross-sectional view of a photovoltaic
electrochromic device according to the third embodiment of the present
invention.

[0027]FIG. 8B is a schematic cross-sectional view of another variation of
the photovoltaic electrochromic device in FIG. 8A.

[0028]FIG. 9 is a block diagram of a photovoltaic electrochromic device
according to the fourth embodiment of the present invention.

[0029]FIG. 10 is a block diagram of another variation of the photovoltaic
electrochromic device in FIG. 9.

[0030]FIG. 11 is a diagram showing a circuit between the photovoltaic
electrochromic device in FIG. 9 and an output switch layout.

[0031]FIG. 12 is a diagram showing a circuit between the photovoltaic
electrochromic device in FIG. 9 and another output switch layout.

[0032]FIG. 13 is a diagram showing a circuit of the photovoltaic
electrochromic device in FIG. 9 and a thin-film transistor.

DESCRIPTION OF EMBODIMENTS

[0033]FIG. 3A is a schematic top view of a photovoltaic electrochromic
device according to the first embodiment of the present invention, and
FIG. 3B illustrates a cross-sectional view thereof along Line B-B in FIG.
3A.

[0034]Referring to FIG. 3A and FIG. 3B, the photovoltaic electrochromic
device in this embodiment is constituted of a semi-transparent thin-film
solar cell substrate 400, a transparent non-conductive substrate 410, and
an electrochromic solution 420. The electrochromic solution 420 is
disposed between the semi-transparent thin-film solar cell substrate 400
and the transparent non-conductive substrate 410, so as to form a
photovoltaic electrochromic device having a single-side conductive
substrate. As shown in FIG. 3B, the semi-transparent thin-film solar cell
substrate 400 has a superstrate structure and includes a transparent
substrate 402 and a plurality of silicon thin-film solar cells 404,
wherein a material of the transparent substrate 402 is glass, plastic, or
other suitable transparent flexible substrates, for example. A material
for forming the transparent non-conductive substrate 410 is, for
instance, glass, plastic, or a flexible substrate. The silicon thin-film
solar cells 404 are formed of an anode 300, a P-type layer 422, an
intrinsic layer 424, an N-type layer 426, and a cathode 310, for example.
Specifically, an anodic material of the anode 300 is, for instance, a
transparent conductive oxide (TCO). The cathode 310 may include a
transparent conductive oxide layer 428 and a metal layer 430, and the
transparent conductive oxide layer 428 of the cathode 310 directly
contacts the N-type layer 426.

[0035]FIG. 3c is a schematic cross-sectional view of another variation of
the photovoltaic electrochromic device in FIG. 3B. As shown in FIG. 3c,
the P-type layer 422, the intrinsic layer 424 and the N-type layer 426
are generally made of semiconductor material, and they are consisted of a
semiconductor stacked layer 432. In FIG. 3c, the semi-transparent
thin-film solar cell substrate 400 further includes passivation layers
434 respectively formed on the sidewalls of each semiconductor stacked
layer 432 so as to protect the semiconductor stacked layer 432 from being
affected by, for example, some electrochromic solutions which may be
corrodible on the semiconductor stacked layer 432. For manufacturing
convenience, the passivation layers 434 may be formed on the sidewalls of
the cathode 310 and the semiconductor stacked layer 432 of each silicon
thin-film solar cells 404.

[0036]In the first embodiment, the electrochromic solution 420 includes at
least one redox-type organic molecule electrochromic material and at
least one solvent, for example, so as to form a solution. Herein, the
redox-type organic molecule electrochromic material is, for example,
selected from one of a cathodic electrochromic material and an anodic
electrochromic material, or a combination thereof. For instance, the
aforesaid cathodic electrochromic material is one selected from the group
consisting of methyl viologen, ethyl viologen, benzyl viologen, heptyl
viologen, propyl viologen, derivatives thereof and a mixture thereof. The
anodic electrochromic material is one selected from the group consisting
of dimethylphenazine, N',N',N',N'-tetramethyl-p-phenylenediamine (TMPD),
phenylene diamine, derivatives thereof and a mixture thereof, for
example. Furthermore, the redox voltages thereof are both smaller than 3V
Moreover, the electrochromic solution 420 may further includes an alkali
metal salt, such as lithium triflate, lithium perchlorate, tetra alkyl
ammonium salt, and so forth. In addition, a proper amount of a polymer,
which is one selected from the group consisting of polyethylene oxide,
polypropylene oxide, polymethylmethacrylate and a mixture thereof, and
the polymer may be added into the electrochromic solution 420 to increase
the viscosity thereof. The solvent in the electrochromic solution 420 may
be propylene carbonate, ethylene carbonate, γ-butyrolactone,
acetonitrile, tetrahydrofuran (THF), or N-methyl-2-pyrrolidone (NMP), for
example.

[0037]The anode 300 and the cathode 310 are not only used as the anodes
and cathodes of the silicon thin-film solar cells 404 but also serve as
the anode and cathode of the photovoltaic electrochromic device in this
embodiment. FIG. 4 is a schematic perspective view of the photovoltaic
electrochromic device in FIG. 3B. When sunlight 500 enters the
photovoltaic electrochromic device through the semi-transparent thin-film
solar cell substrate 400, the thin-film solar cells (refer to 404 in FIG.
3B) simultaneously generate electron-hole pairs. During the generation of
electricity, current outputted from the thin-film solar cells is
transmitted to the electrochromic solution 420 through the anode 300 and
the cathode 310, which causes a redox reaction within the transparent and
colorless electrochromic solution 420. At the same time, the constitution
of the anode 300, the cathode 310, and the electrochromic solution 420
immediately functioning as electrochromic device. After the cathode 310
receives electrons released from the thin-film solar cells, reduction
occurs and the color of the cathodic electrochromic material changes.
After the anode 300 receives holes released from the thin-film solar
cells, oxidization occurs and the color of the anodic electrochromic
material changes. In addition, a reflective layer 510a or 510b maybe
deposited on the transparent non-conductive substrate 410 to form a
mirror surface; for example, a material of the reflective layer 510a or
510b includes one of silver and aluminum thin film coatings.

[0038]When the intensity of the sunlight declines, the electrons and holes
generated by the thin-film solar cells are reduced and the current
generates by the photovoltaic electrochromic device decreases gradually.
The color of the cathodic electrochromic material on a surface of the
cathode 310 gradually fades out and returns to the transparent and
colorless oxidized state. The color of the anodic electrochromic material
on a surface of the anode 300 also gradually fades out and returns the
transparent and colorless reduced state. The electronic current generated
by the thin-film solar cells is converted into an ionic current in the
electrochromic solution 420. Thus, even though the anode 300 and the
cathode 310 both contact the electrochromic solution 420 when conducted,
the problem of short circuit would not occur. To maintain a charge
balance in the redox reaction of the anode and the cathode during color
changing, the area ratio of the anode 300 and the cathode 310 is
preferably similar.

[0039]In this embodiment, the electrochromic solution 420 merely requires
a low voltage and a low current to change color. For instance, 0.01M of
methyl viologen dichloride and 0.1M of lithium. perchlorate are added and
dissolved in 5 milliliter DI water first. After stirring, a well-mixed
and colorless electrochromic solution is obtained. The aforesaid methyl
viologen dichloride is 1,1'-dimethyl-4,4'-bipyridinium dichloride, which
is represented by the following formula:

##STR00001##

[0040]Next, the electrochromic solution is applied onto an
indium-tin-oxide (ITO) conductive glass substrate of an area 2 cm×2
cm. Further, another indium-tin-oxide conductive glass substrate is added
thereon to form an electrochromic device. An anode and a cathode of the
electrochromic device are connected to an electrochemistry analyzer for
performing a cyclic voltammogram (CV) scan from -1V to 3V. The scan
result is shown in FIG. 5. General organic molecules require a fairly low
redox voltage. Take the cathodic electrochromic material formed of
viologen group as an example, an obvious color contrast is achieved when
a charge density reaches 2 mC/cm2.

[0041]With reference to FIG. 3B, because the redox voltage of the
electrochromic solution 420 is low and the charge density required for
color changing is not high, the transparent conductive oxide layer 428 is
sufficient to serve as the cathode 310 when the thin-film solar cells 404
generate enough electricity for color changing. Moreover, the thickness
of the intrinsic layer 424 can be reduced to increase the transmittance
of the whole photovoltaic electrochromic device.

[0042]The following experimental examples are given to support the
applicability of the photovoltaic electrochromic device in this
embodiment.

EXPERIMENTAL EXAMPLE 1

[0043]A transparent glass substrate is first provided. Then, 0.1M of
lithium perchlorate and 0.01M of methyl viologen
(1,1'-dimethyl-4,4'-bipyridinium dichloride) are dissolved in 5
milliliter DI water and stirred to obtain a well-mixed transparent and
colorless electrochromic solution. The electrochromic solution is applied
to the aforesaid transparent glass substrate, and a semi-transparent
thin-film solar cell substrate having an area of 15 cm×15 cm is
attached onto the transparent glass substrate by an epoxy resin adhesive.
Silicon thin-film solar cells are used in this example. The silicon
thin-film solar cells are arranged in array, and one single array has an
area of 0.25 cm2. The epoxy resin adhesive has a thickness of around
0.15 centimeters and is mixed with glass beads which serve as spacers to
maintain a distance between two substrates.

[0044]To be more detailed, the semi-transparent thin-film solar cell
substrate may be formed by a sputtering process, which is to grow a
transparent conductive layer on a glass substrate of 15 cm×15 cm,
follows by continuously depositing silicon thin films on the transparent
conductive glass layer by a plasma enhanced chemical vapor deposition
process, and finally a transparent conductive layer and a metal layer are
sputtered on the silicon thin films. Thereafter, a pulse laser of 532 nm
is used to remove a portion of the aforesaid silicon thin films, so as to
form silicon thin-film solar cells arranged in array, wherein cathode
blocks are silicon thin films each having an area of 0.5 cm×0.5 cm,
and the areas outside the cathode blocks are anodic. Each of the cathode
block is separated by a gap of 0.2 cm, and the total number of the
cathode blocks is 196. As shown in FIG. 6, a structure thereof includes a
glass substrate 600 having an area of 15×15 cm2; a ZnO:Al
layer 602 which serves as the anode and has a thickness of 10 nm; a
P-type layer 604 having a thickness of 30 nm; an a-SiH layer 606 which
serves as the intrinsic layer and has a thickness of 450 nm; an N-type
layer 608 which has a thickness of 30 nm; and a ZnO:Al layer 610 of 80 nm
thick and an Ag layer 612 of 300 nm thick which together constitute the
cathode.

[0045]An open circuit voltage (Voc) of the semi-transparent thin-film
solar cells is 0.6V. The current density Jsc is 5 mA/cm2 and a Pmax
is 0.5 mW. When sunlight irradiates upon the photovoltaic electrochromic
device, the electrochromic solution right beneath the cathode starts to
change color from transparent and colorless to light blue and then to
deep blue within 30 seconds. When the sunlight is stopped, the
photovoltaic electrochromic device restores transparency within 15
seconds.

EXPERIMENTAL EXAMPLE 2

[0046]A transparent glass substrate is first provided. Then, 0.1M of
lithium perchlorate, 0.01M of 5,10-dihydro-5,10-dimethyl phenazine is
dissolved into 5 milliliters of propylene carbonate solvent and stirred
to obtain a well-mixed transparent and colorless electrochromic solution.
The electrochromic solution is applied to the aforesaid transparent glass
substrate, and a semi-transparent thin-film solar cell substrate having
an area of 15 cm×15 cm is attached onto the transparent glass
substrate by an epoxy resin adhesive. Silicon thin-film solar cells
arranged in array are used in this experimental example. Each array has
an area of 0.25 cm2 and has a structure identical to the structure
mentioned in experimental example 1. A thickness of the epoxy resin
adhesive is about 0.15 centimeters and glass beads which serve as spacers
are mixed thereinto, so as to maintain a distance between two substrates.

[0047]The open circuit voltage (Voc) of the semi-transparent thin-film
solar cells is 0.62V. The current density Jsc is 5.2 mA/cm2 and the
Pmax is 0.55 mW. Accordingly, when sunlight irradiates upon the
photovoltaic electrochromic device, the electrochromic solution right
beneath the anode starts to change color from transparent and light
yellow to yellow and then to green within 40 seconds. When the sunlight
is stopped, the photovoltaic electrochromic device becomes transparent
and light yellow within 20 seconds.

EXPERIMENTAL EXAMPLE 3

[0048]A transparent glass substrate having an area of 7.5 cm×7.5 cm
is first provided, and then edges of the transparent glass substrate is
pasted with solvent resistant tape which serve as spacers. Thereafter,
0.01M of Heptyl Viologen and 0.01M of TMPD are dissolved in propylene
carbonate, and then 0.1M of TBABF4 of electrolyte salt is added.
After that, the above mixture is stirred to obtain a well-mixed
transparent and colorless electrochromic solution. The electrochromic
solution is applied to the aforesaid transparent glass substrate, and a
semi-transparent thin-film solar cell substrate having an area of 7.5
cm×7.5 cm is attached onto the transparent glass substrate so as to
constitute a photovoltaic electrochromic device.

[0049]Silicon thin-film solar cells arranged in stripe are used in this
experimental example, wherein cathode blocks are silicon thin films each
having an area of 5 cm×1 cm, and the areas outside the cathode
blocks are anodic. Each of the cathode block is separated by a gap of 1
cm, and the total number of the cathode blocks is 3.

[0050]The open circuit voltage (Voc) of the semi-transparent thin-film
solar cells is 0.64V. The current density Jsc is 5.7 mA/cm2.
Accordingly, when sunlight irradiates upon the photovoltaic
electrochromic device, the electrochromic solution right beneath the
anode and cathode start to change color from transparent to deep blue
within 30 sec.

[0051]FIG. 7A is a schematic cross-sectional view of a photovoltaic
electrochromic device according to the second embodiment of the present
invention, in which identical elements are indicated by the same
reference numbers as in the first embodiment. Referring to FIG. 7A, the
photovoltaic electrochromic device in the second embodiment is
constituted of a semi-transparent thin-film solar cell substrate 700, the
electrochromic solution 420, and the transparent non-conductive substrate
410. The aforesaid semi-transparent thin-film solar cell substrate 700
has a substrate structure (i.e. the sunlight 500 enters through the
transparent non-conductive substrate 410) and includes the silicon
thin-film solar cells 404 and the transparent substrate 402. Further, the
silicon thin-film solar cells 404 are formed of the cathode 310, the
N-type layer 426, the intrinsic layer 424, the P-type layer 422, and the
anode 300. Herein, the material for forming the anode 300 is, for
example, a transparent conductive oxide (TCO). The cathode 310 may
include a transparent conductive oxide layer 428 and a metal layer 430
disposed between the N-type layer 426 and the transparent conductive
oxide layer 428. Because the semi-transparent thin-film solar cell
substrate 700 has the substrate structure, the color changing of the
electrochromic solution 420 may affect the conditions for the silicon
thin-film solar cells 404 to generate electricity. For this reason, the
photovoltaic electrochromic device in the second embodiment is applicable
to devices which require cyclic color changing.

[0052]FIG. 7B is a schematic cross-sectional view of another variation of
the photovoltaic electrochromic device in FIG. 7A. As shown in FIG. 7B,
the P-type layer 422, the intrinsic layer 424 and the N-type layer 426
are consisted of a semiconductor stacked layer 432, for example.
Moreover, the semi-transparent thin-film solar cell substrate 700 further
includes passivation layers 434 respectively formed on the sidewalls of
each semiconductor stacked layer 432 to protect the semiconductor stacked
layer 432 from being affected by some electrochromic solutions. In
addition, the passivation layers 434 may be formed on the sidewalls of
the anode 300, the metal layer 430 and the semiconductor stacked layer
432 of each silicon thin-film solar cells 404 for manufacturing
convenience.

[0053]FIG. 8A is a schematic cross-sectional view of a photovoltaic
electrochromic device according to the third embodiment of the present
invention, in which identical elements indicated by reference numbers are
the same as those in the second embodiment. With reference to FIG. 8, the
main difference between the photovoltaic electrochromic devices in the
second and the third embodiments lies in that a semi-transparent
thin-film solar cell substrate 800 in the third embodiment includes the
transparent substrate 402 and a plurality of CIGS thin-film solar cells
802, wherein the CIGS thin-film solar cells 802 are formed by the anode
300, a CIGS absorber layer 804, a buffer layer 806, and the cathode 310.
A material of the anode 300 and the cathode 310 is a transparent
conductive oxide (TCO), for example. Moreover, CdTe thin-film solar cells
may also be used in the third embodiment.

[0054]FIG. 8B is a schematic cross-sectional view of another variation of
the photovoltaic electrochromic device in FIG. 8A. As shown in FIG. 8B,
the semi-transparent thin-film solar cell substrate 800 further includes
passivation layers 434 respectively formed on the sidewalls of the CIGS
absorber layer 804, the buffer layer 806 and the cathode 310. This
passivation layers 434 at least have protective function to the CIGS
absorber layer 804 and the buffer layer 806.

[0055]FIG. 9 is a block diagram of a photovoltaic electrochromic device
according to the fourth embodiment of the present invention. With
reference to FIG. 9, in addition to the semi-transparent thin-film solar
cell substrate (ex. 400 in FIG. 4, 700 in FIGS. 7A-7B and 800 in FIGS.
8A-8B), the electrochromic solution (ex. 420 in FIG. 4), and the
transparent non-conductive substrate (ex. 410 in FIG. 4) in the above
embodiments, the photovoltaic electrochromic device in this embodiment
further includes an output switch layout 900 connected to the thin-film
solar cells (ex. 404 in FIG. 3B and 802 in FIG. 8A) for connecting the
anode 300 with the cathode 310 to control a current output from the
thin-film solar cells 404. Descriptions of the elements of the
photovoltaic electrochromic device in this embodiment may be referred to
in the above embodiments and therefore not repeated hereinafter.

[0056]FIG. 9 illustrates a parallel connection, wherein the anode 300 of
the thin-film solar cells is a continuous film connected with the output
switch layout 900. Further, the anode 300 and the cathodes 310a, 310b,
310c, and 310d which are arranged in stripe are respectively connected to
the output switch layout 900.

[0057]Besides the parallel connection in FIG. 9, the output switch layout
900 may also be connected in series as shown in FIG. 10, wherein the
discontinuous anodes 300b, 300c, and 300d are connected with the cathodes
310a, 310b, and 310c of another thin-film solar cell, and the anode 300a
and the cathode 310d are connected with the output switch layout 900.

[0058]The aforesaid output switch layout 900 may be fabricated based on
technology that is currently available. For instance, FIG. 11 and FIG. 12
are diagrams respectively showing the circuits between the photovoltaic
electrochromic device in FIG. 9 and different output switch layouts.

[0059]Referring to FIG. 11, the reference number 1100 represents an
electrochromic device of the photovoltaic electrochromic device in FIG. 9
(or FIG. 10). The electrochromic device 1100 and a thin-film solar cell
1102 are connected to a DC/AC inverter 1104. When a switch 1106 is
connected, a current outputted by the thin-film solar cell 1102 is
converted into general electricity 1108 (i.e. alternating current) for AC
electric appliances.

[0060]Furthermore, referring to FIG. 12, the electrochromic device 1100
and the thin-film solar cell 1102 may be connected to a DC charge storage
device 1200 (electricity storage device), so as to store a direct current
generated by the thin-film solar cell 1102 for use of DC electrical
appliances. When the switch 1106 is connected, the electrochromic device
1100 returns to colorless state.

[0061]In addition, the photovoltaic electrochromic device in FIG. 9 (or
FIG. 10) may be combined with thin-film transistor (TFT) technology,
wherein a thin-film transistor 1300 is disposed on the semi-transparent
thin-film solar cell substrate, as shown in the circuit diagram of FIG.
13, so as to actively control the thin-film solar cell 1102 and
manipulate the color changing of the electrochromic device 1100.

[0062]As above, the present invention has at least the following
advantages:

[0063]In the present invention, the current generated by the photovoltaic
electrochromic device is converted into an ion current in the
electrochromic solution. Even though the anode and the cathode contact
simultaneously when connected, short circuit would not occur.

[0064]The electrodes in the photovoltaic electrochromic device of the
present invention are different from the conventional electrochromic
device, in which electricity is supplied by periphery of the electrode.
According to the present invention, the electrodes are evenly distributed
in the whole semi-transparent thin-film solar cell substrate to create a
uniform electric field. Therefore, the electrochromic solution in
different areas still performs the same color change, and the iris effect
is prevented.

[0065]In the present invention, redox-type organic molecule electrochromic
material which has redox voltage smaller than 3V is adopted to form the
photovoltaic electrochromic device. Accordingly, the photovoltaic
electrochromic device can be driven with low voltage and low current.
Furthermore, the thickness of the intrinsic layer of the thin-film solar
cells is reduced, and merely the transparent conductive oxide layer is
used as the electrode. As a consequence, the light transmittance of the
device is increased, and the application of the device is extended to
further reduce the production costs of the device.

[0066]The photovoltaic electrochromic device of the present invention may
further include the output switch layout for connecting the DC/AC
inverter and the DC charge storage device, so as to supply AC and DC
electric appliances with the current generated by the device. It is one
of the solutions to the problem of energy shortage.

[0067]Although the present invention has been disclosed by the above
embodiments, they are not intended to limit the present invention.
Persons having ordinary knowledge in the art may make some modifications
and variations without departing from the spirit and scope of the present
invention. Therefore, the protection sought by the present invention
falls in the appended claims.